Rename Janus-specific restream fields to be more generic since they are
now used by Go2RTC and RTSP2Web as well:
- Janus_Use_RTSP_Restream → Restream
- Janus_RTSP_User → RTSP_User
Update visibility logic so the Restream checkbox appears when RTSPServer
is enabled AND any streaming service (Janus, Go2RTC, or RTSP2Web) is
selected, rather than only when Janus is enabled.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>